Muscle weakness and mobility impairment are important risk factors for falls in the frail elderly. Marked decreases in muscle strength may be attributable to: 1) biological changes of aging, 2) acute and chronic diseases, 3) sedentary lifestyle and 4) selective or generalized nutritional inadequacies. Inactivity and undernutrition are potentially reversible with appropriate intervention. We postulate that improved muscle strength through exercise and nutrition will result in improved clinical and functional status and reduced risk of falls. The goals of this study are: 1) To characterize muscle function in the elderly with a history of recurrent falls, and 2) to perform a trial of vigorous progressive resistance training of the leg muscles and/or multi- nutrient supplementation, in order to improve muscle strength and mobility. One hundred frail institutionalized fallers aged 80-99 will be recruited from the Hebrew Rehabilitation Center for Aged (HCRA). Using a blinded randomized design, subjects will participate in one of four ten-week interventions: 1) placebo and sedentary activity group, 2) nutritional supplement and sedentary activity group, 3) placebo and strength training, or 4) nutritional supplement and strength training. Clinical and functional correlates of muscle performance will be assessed by mobility, gait and balance, falls, acute illnesses and medication use, activities of daily living, and mental status. Since muscle mass is closely related to strength, body composition will be measured by anthropometry, whole body potassium, total body water, bioelectric impedance, and CT scan. The histological and biochemical characteristics of muscle will be determined in a biopsy from m. vastus lateralis. Muscle function will be measured in knee and hip extensions as the maximum load that can voluntarily be lifted (the one repetition maximum, or 1RM). Adductor pollicis stimulation will be used to determine contractility characteristics. Habitual level of physical activity will be quantified by average daily energy expenditure, using the new, objective technique of doubly-labeled water, as well as movements/day from activity monitors. Three-day food weighing, body composition and blood nutritional profile will be used to determine relationships between nutrient intake, nutritional status, and muscle function. This study will provide important data on the feasibility and efficacy of new strategies for improving functional independence and reducing falls in this population.